Carbon-carbon materials are produced starting with organic precursor fibers such as polyacrylonitrile, rayon or pitch. Such fibers are usually produced in bundles (roving or yarn), often by an extrusion process. The precursor fibers are heated in an inert atmosphere to pyrolyze or carbonize them and may then be heated to a higher temperature (e.g. greater than 4000.degree. F., 2204.degree. C.) to form graphite fibers. These carbon or graphite materials may then be laid down, woven, or interleaved to form what are referred to as 1D, 2D, 3D, . . . nD etc. structures where D stands for direction and n stands for number of directions (i.e. in a 2D structure fibers are laid in two (typically orthogonal) directions).
These woven structures can then be cut to the length and width desired to form composite components (e.g. gas turbine engine components, aircraft brakes, rocket nozzles) and then stacked in a die or on a mold for treatment. The woven structures can be stacked with alternate layers of resin or pitch material or preferably the woven structures may be first impregnated with the resin, typically under pressure, and then laid up on a form or stacked in a mold to form a prepreg. The material is then heated to cure the resin binder forming a fiber reinforced precursor composite part. The part is then pyrolyzed and sometimes graphitized. Optional repeated impregnation steps followed by pyrolysis and graphitization steps can be employed to increase density (e.g. redensification). An alternative processing scheme is to use CVD to deposit pyrolytic graphite to densify the structure after the initial cure and carbonization cycles have been done.
There can be problems with present carbon-carbon manufacturing processes because during the molding and subsequent steps (e.g. curing, post-curing and pyrolization). For example, resin shrinkage in the composite can cause internal stresses, resulting in delaminations and cracking.
Accordingly, there has been a constant search for improved methods of molding carbon-carbon composites.